Artificial respiration with respirators is aimed at relieving the respiratory muscles of a patient and at guaranteeing a sufficient supply of oxygen and elimination of carbon dioxide. This can happen by complete takeover of the breathing activity by the respirator or in an assisting process by partial takeover of breathing activity by the respirator, whereby in the latter assisting process, a present breathing activity of the patient is assisted or reinforced. For this, the respirators contain a fan for supplying breathing gas with a pressure, which is preset by a control unit. Furthermore, sensors are present, which detect pneumatic breathing signals in a time-dependent manner, for example, airway pressure, volume flow (flow) of the breathing gas and volume (which results from the integration of the flow), and forward these to the control unit.
In view of the rise in chronic lung diseases and the demand for an improved therapy, noninvasive breathing assistance with improved interaction of the patient and fan is a decisive requirement of modern respirators. An essential object herein is to establish time-based synchronicity between the device-side assistance and the patient's own breathing activity. Spontaneously breathing patients were frequently sedated in the past to adjust the respiration correctly and to force synchronicity between patient and respirator. This procedure is no longer acceptable by today's knowledge since risks of lung damage caused by the respiration have to be dealt with.
For an improved synchronization between the breathing activity of the patient and the fan action, it is important to detect the beginning of inspiration and the beginning of expiration in the breathing activity of the patient early and reliably. The breathing phase detection is especially often incorrect or late in newborns and in Chronic Obstructive Pulmonary Disease (COPD) patients using conventional processes and leads to increased respiratory work until exhaustion.
For an artificial respiration which shall take the patient's breathing activity into consideration in an improved manner, it is known from DE 10 2007 062 214 B3 to pick up electromyographic signals, besides pneumatic breathing activity signals, by means of electrodes placed on the thorax and to derive electromyographic breathing activity signals (EMG signals) therefrom. These EMG signals are independent of the pneumatic breathing activity signals and therefore represent an independent source of information, which can be used to detect the beginning of inspiration and expiration. The EMG signals are, however, not infrequently superimposed by interference, for example, the ECG signal of the heart, motion artifacts or so-called cross-talk (muscle activity that has nothing to do with the respiratory system of the patient).
A triggering of breaths on the basis of EMG signals is described in U.S. Pat. No. 6,588,423 B1. Here, the EMG raw signal is preprocessed and is finally used for triggering an intensity indicator (root mean square) of the EMG signal, whereby a fixed threshold is used—related to one breath.
In practice, however, the preprocessed EMG signal is often more susceptible to interference than pneumatic signals (pressure or volume flow). Such a susceptibility to interference or volatility makes it more difficult to change over or trigger the breaths when using trigger thresholds, since too many breaths may be mistakenly triggered (so-called autotrigger) or may be triggered too late (so-called delayed or missed trigger).
Marking of the signals with interference can be avoided by suitable filterings (e.g., by means of sliding averaging) of the signals. However, this would result in the major drawback of an additional signal delay for the intended use for changing over between phases of respiration.
In DE 102 12 497 A1, it is generally pointed out that at the beginning of a phase of inspiration, a continuation of the inspiration phase is essentially more likely than its premature end, and that a new beginning of an inspiration phase has a higher probability shortly before an end of the phase of expiration. Basically, it means that with an increasing probability for the development of an event triggering the phase of respiration, the trigger threshold can be lowered, since the influence of interference is unlikely, on the one hand, and moreover, even in case of a mistriggering based on a developing interference, the result of this erroneous changeover is markedly less interfering because of the chronological closeness to a correct changeover point in time than an erroneous changeover at a completely incorrect point in time. Moreover, no further indications are, however, made as to how and with what time curve and up to what chronological point in time a dynamic threshold curve shall be performed chronologically.